1. Field of the Invention
The present invention relates to devices used to measure temperatures in rapid thermal processing tools for silicon wafer processing and, more particularly, to a thin-film thermocouple calibration wafer for calibrating pyrometric temperatures.
2. Related Art
Rapid thermal processing (RTP) technology is becoming more widely used in the fabrication of semiconductor integrated circuits because of its ability to obtain smaller feature sizes on semiconductor chips, its reduced development and production times, and its adaptability to changes in wafer size and design. In particular, RTP technology is used in processes including dopant anneal, polysilicon deposition, and chemical vapor deposition of metals, silicides and nitrides. However, RTP tools require more stringent temperature control than other semiconductor fabrication devices. Conventional calibration wafers with wire thermocouples have demonstrated poorly defined effects on the heat transfer to the wafer during the calibration procedure and lack the accuracy required. The insulation layer between the wafer and the wires and the conductivity of the wires disturb the heat transfer pattern leading to uncertainties in the temperature measurement.
Thin-film thermocouples have been used in applications where wire thermocouples are not suitable. However, the use of thin-film thermocouples at elevated temperatures has been limited because the reactivity of thin-film thermocouples is more of a problem than with conventional wire thermocouples. Reactivity is more of a problem because of the very short diffusion distances present in thin-films. For example, what might be considered a small surface reaction on a wire can consume a 1 .mu.m thick film. The chemical reactions of the thin-films lead to a change in the Seebeck coefficient. The problem of reactivity increases at high temperatures, such as those encountered in RTP tools for silicon wafer processing. RTP tools reach temperatures up to 900.degree. C. Thin-film thermocouples have not been used with RTP technology because of the reactivity problem with silicon wafers and other reasons.
Therefore, there exists a need in the art for a thin-film thermocouple which can be used on silicon wafers at temperatures of up to 900.degree. C.